The long range objective of this project is the description of the component molecular events involved in the replication of the negative strand viruses (myxo, paramyxo and rhabdo viruses). The topics that are currently being investigated are: 1) The mechanism of autointerference by defective interfering (DI) particles. 2) The nucleotide sequence of DI RNA. 3) Consequences of the presence of DI particles in infected cells.